Final answer:
The frequency heard by the person on the railcar depends on the relative speeds of the railcar and the horn.
Step-by-step explanation:
The frequency that the person on the railcar hears, denoted as f', can be calculated using the Doppler effect equation. If the railcar is moving away from the horn, the frequency heard by the person on the railcar will be lower than the emitted frequency. If the railcar is moving towards the horn, the frequency heard will be higher than the emitted frequency.
The Doppler effect equation is given by:
f' = f imes (v + vr) / (v + vs)
Where f is the emitted frequency, v is the speed of sound, vr is the speed of the railcar, and vs is the speed of the horn.
For example, if the railcar is moving away from the horn, the frequency heard by the person on the railcar will be lower than the emitted frequency.